The Trailians were a sentient species of humanoids. They were all Force-sensitive with a great deal of raw potential and had great physical beauty.
The Trailians had a low technology society. They lived in villages, dwelling in harmony with their world's environment. What little technology they did have consisted of adaptations of what already occurred in nature. Culturally, the Trailians were a peaceful people; however, once experimented upon, they became powerful warriors with devastating combat and force abilities.
Cronal twisted his Trailian subjects into ferocious warriors.
The Trailians evolved on Trailia, a lush tropical planet in the distant Dominus sector of the Outer Rim Territories, near the Dark Nebula. They had developed a peaceful, low technology society by the time of the New Republic. However, that existence was disturbed when Cronal, one of Galactic Emperor Palpatine's most powerful dark side servants and an Emperor's Hand, discovered the planet sometime after his exile. He established a hidden laboratory deep within the planet's jungles and began to capture native Trailians.
Using a combination of genetic engineering and dark side experimentation, Cronal twisted his captives into a savage race of Trailian sithspawn, hoping to use them to crush the New Republic. While some of those warriors were kept to guard his fortress where an army of them was being prepared alongside animals he had similarly twisted, Cronal dispatched warriors on missions to other worlds to test their combat skills. Word of unprovoked raids by those warriors on unsuspecting planets soon spread, and the remaining peaceful Trailians grew concerned about the increasing disappearances of their people. They offered a reward to anyone who would investigate, which attracted a group of offworlders to Trailia.
The offworlders included a Force-sensitive individual who was able to detect the dark side emanating from Cronal's fortress and lead the group to it. In a climactic battle, they defeated the twisted Trailian guards and other beasts and routed the fortress. Cronal, however, escaped the battle. Similarly, some of his warriors found transport offworld and continued razing offworld cities until the same group of offworlders tracked them down and defeated them.
As for Cronal, he fled to the bowels planet Coruscant, accompanied by several of his finest Trailian technobeasts. These Trailians were later killed when Cronal tried to transform the Human Irek Ismaren into a colossal cyborg warrior, leading to the newly-modified Ismaren going on a violent rampage.
The Trailians were created by Bill Olmesdahl for the Star Wars Gamemaster Screen, a West End Games product for the second edition of their role-playing game. Published in 1992, the book contains adventure hooks to be fleshed out by game masters. The Trailian adventure is titled "The Monster Maker." In addition to the main proposed storyline, Olmesdahl offers an extension in which twisted Trailians make it offworld and the player-characters encounter them on other worlds. This has been incorporated into the above storyline as an extension to the main campaign.
No date is provided for Cronal's experiments on the planet; however, it is during the administration of the New Republic and therefore after its founding in 5 ABY. In later sources, Cronal has been identified as both Blackhole and Lord Shadowspawn. As he is still alive up until at least 9 ABY, this adventure could occur anytime during the New Republic era.